1. Field of the Invention
The present disclosure relates to a pressure balanced drilling system and method of controlling a pressure kick using the pressure balanced drilling system.
2. Description of the Related Art
The exploration and production of hydrocarbons from subsurface formations ultimately requires a method to reach and extract the hydrocarbons from the formation. This may be achieved by drilling a well with a drilling rig. In its simplest form, the drilling rig supports a rotatable drill string, which includes a drill bit mounted at the end of the rotatable drill string. The drill bit drills a well bore which is lined with a well casing. A pumping system is used to circulate a drilling fluid down the center of the drill string. The drilling fluid then exits the drill string through the drill bit and flows back to the surface through an annular space between the drill string and the well casing. The drilling fluid has multiple functions, including providing pressure in the well bore to prevent the influx of a fluid from the formation, to provide support to the borehole wall, to transport cuttings produced by the drill bit to the surface, to provide hydraulic power to tools fixed in the drill string, and to cool the drill bit.
A blowout preventer (“BOP”) is generally used to seal a well bore. For example, drilling an oil or gas exploration well involves penetrating a variety of subsurface geologic structures, or “layers.” Each layer generally includes a specific geologic composition such as, for example, shale, sandstone, or limestone. Each layer may contain a trapped fluid at a different formation pressure, and the formation pressures generally increase with increasing depth. The pressure in the well bore may be selected to at least balance the formation pressure by, for example, increasing a density of drilling mud in the well bore or increasing a pump pressure at the surface of the well.
There are occasions during drilling operations when the well bore may penetrate a layer having a formation pressure substantially higher than the pressure maintained in the well bore. When this occurs, the well is said to have “taken a kick,” which is a spontaneous influx of a fluid, which may include a liquid, a gas, or a combination thereof, from the formation into the well bore. The pressure increase associated with the kick is generally produced by an influx of the fluid from the formation into the well bore. The relatively high pressure kick tends to propagate from a point of entry in the well bore up-hole (e.g., from a high pressure region to a low pressure region). In particular, because the drilling fluid is commonly circulated down the hollow drill string and up through the annular volume surrounding the drill string, gases, which may be contained in the drilling fluid, expand as they are moved towards lower pressure regions nearer the surface. The gas expansion may cause the kick to accelerate uncontrollably. Also, if the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the well-bore, resulting in a “blowout.” A blowout often results in catastrophic destruction of the drilling equipment, including, for example, the drilling rig, and can result in substantial injury or the death of rig personnel.
In the event of a kick, the blowout preventer may be closed to prevent the release of fluid from the well and to stop further influx of fluid from the formation into the well. However, despite use of commercially available BOPs, and other devices, blowouts still occur. Further, recent blowouts have demonstrated that commercially available BOPs, in particular those used in offshore wells, either close the well too slowly to be effective, or are insufficiently reliable. Also, current methods of controlling and managing kicks result in undesirable down-time, increasing the cost of drilling a well. Therefore there remains a need for an improved well drilling system which provides improved well pressure control and provides a more reliable method of managing kicks.